This invention relates generally to liners for milking machine teat cups, and more particularly to improved teat cup liners that provide a superior seal against a teat upper portion and a controlled collapse around a teat lower portion to reduce tissue irritation and damage while enhancing the milking process.
Dairy animals, and particularly cows, are milked using automated milking machines. The milking machines include a milking unit including four teat cups, tubes downstream from the teat cups, a claw that acts as a manifold connected to the tubes for receiving milk, a pulsator, and pulsation tubes. The milking machines connect downstream with equipment for collecting milk.
The interface between milking machine and animal is a flexible liner inside a teat cup. A teat fits inside the liner during milking. An annular space between the liner and the teat cup is called a pulsation chamber. Vacuum from a vacuum pump is controlled by the pulsator to provide the pulsation of vacuum and pressure necessary to withdraw milk from the teats. A continuous vacuum is applied inside the liner to withdraw milk and keeps the milking unit attached to a cow. The continuous vacuum causes congestion of blood and other fluids in teat tissue. To relieve this congestion, atmospheric air is allowed into the pulsation chamber by the pulsator so that the flexible liner collapses onto the teat to relieve the congestion in the teat tissue. This pulsating action efficiently milks dairy animals.
The liner design is critical to obtaining efficient and complete milking while simultaneously providing maximum comfort and minimal irritation to the animal teats. Liners include at least two key components. First, is an upper dome portion and second is a lower barrel portion. Some liners include short tubes extending downstream from the liner barrel to connect to the milking claw. Other liners are designed to be connected to a separate short milk tube.
The upper dome portion includes an upper surface defining an opening through which a teat is inserted. The dome also includes an outer cylindrical wall with a lip to engage a teat cup. The dome defines an inner volume in which the vacuum acts to hold the milking unit on the animals. The shape and volume of liner domes have been studied for applying optimum vacuum and pressure to teats. (See U.S. Pat. No. 5,752,462.)
Liner barrels too have been the subject of considerable study. A basic liner barrel is cylindrical and essentially round in cross-section. When atmospheric pressure is applied in the pulsation chamber against the outer surface of the liner barrel, it collapses by flattening into a tight oval shape, and thereby applies pressure from two sides against a teat. Since teats are essentially round in cross-section, the application of pressure from two sides can cause undue stress, irritation, and excessive pressure on teat tissue.
In U.S. Pat. No. 3,967,587, the above problem with round barrels was addressed with a liner barrel having a square cross-section so that pressure was applied from four sides instead of two. The total pressure applied to a liner is the same regardless of whether the liner barrel is round or square in cross-section, so applying that pressure from four sides instead of two reduced the pressure and irritation on the teat by about one half.
One downside to a square-barreled liner is that during the vacuum phase, the teat tissue tends to expand into the corners of the square barrel and cause irritation of teat tissue. Further, the milking machine teat cups are held onto a teat by the vacuum in the liner. Therefore, a seal between teat and liner is necessary so that the milking machine does not fall off the cow during milking. Barrel liners with square cross-sections tend not to form as secure a seal with teats, and premature release can occur.
Thus, there is a need for a milking machine teat cup liner that will form a secure seal with a dairy animal teat, while simultaneously applying relatively uniform and gentle pressure to a teat for milking.